This invention relates to an arrangement for use in a broadband integrated services digital network (ISDN) to arrange a connection path or a route between a plurality of input paths and a plurality of output paths.
Such a broadband ISDN is effective to provide a wide variety of services for communication of an audio signal, a video signal, and a data signal. Recently, it has been pointed out that the broadband ISDN is preferably operable in an asynchronous transfer mode (ATM) wherein a transmission data signal to be delivered to an identical destination asynchronously or unperiodically appears on a transmission line. In this event, each transmission data signal is transmitted in the form of a cell. Such a cell may be called an asynchronous transfer mode cell.
In order to identify a logical path of each asynchronous transfer mode cell, a virtual channel identifier (VCI) is included in each asynchronous transfer mode cell to relatively specify a logical channel number used in the logical path. In other words, the virtual channel identifier never specifies a physical channel number or a physical path. This shows that, when identical virtual channel identifiers are produced from different terminal units, such identical virtual channel identifiers are transmitted through different transmission paths. From this fact, it is readily understood that each identical virtual channel identifier is regardless of each other as long as such identical virtual channel identifiers are transmitted through different transmission paths.
At any rate, each asynchronous transfer mode cell is given to an asynchronous transfer mode exchange, namely, an arrangement which is located between a plurality of input paths and a plurality of output paths to arrange a connection path or a route between the input and the output paths. In this case, an input asynchronous transfer mode cell is sent to the asynchronous transfer mode exchange through one of the input paths along with an input virtual channel identifier and is transmitted through a selected one of the output paths that is determined by the asynchronous transfer mode exchange. Thus, an output asynchronous transfer mode cell is sent from the asynchronous transfer mode exchange together with an output virtual channel identifier. In this event, the asynchronous transfer mode exchange carries out a self-routing switching operation so as to decide the route between the input and the output paths.
Herein, it is to be noted that the input virtual channel identifier is usually different from the output virtual channel identifier and should therefore be converted in the asynchronous transfer mode exchange into the output virtual channel identifier which is sent through one of the output paths.
To this end, conversion of the input virtual channel identifier into the output virtual channel identifier is performed before the self-routing switching operation in a conventional asynchronous transfer mode system that is described in a paper contributed by K. Hajikano et al and entitled "Asynchronous transfer mode switching architecture for broadband ISDN" (pages 911 to 915) to IEEE International Conference on Communications '88. Such conversion is effective to selectively connect a single one of the input paths to a single one of the output paths. A connection between a single input path and a single output path and its operation will be called a one-to-one connection and a one-to-one connection mode.
Herein, the connection is not always restricted to the one-to-one connection but may be made between a single input path and a plurality of output paths which are equal in number to N, where N is a natural number. The connection between the single input path and the N output paths and its operation will be referred to as a one-to-N connection hereinafter. The one-to-N connection lends itself to simultaneously transfer information from a single terminal unit or transmitting end to a plurality of terminal units or receiving ends. Stated otherwise, it is possible to broadcast the information to the plurality of the receiving ends during a mode of the one-to-N connection. Such a mode may therefore be called a broadcast mode.
Let the conventional asynchronous transfer mode system be operated in the broadcast mode in response to the input asynchronous transfer mode cell which includes the single input virtual channel identifier and which is given through a single one of the input paths. Under the circumstances, the single input virtual channel identifier should be converted before the self-routing switching operation into a plurality of output virtual channel identifiers which are different from and independent of one another.
However, it is difficult to convert the single input virtual channel identifier into the plurality of the output virtual channel identifiers on the single input path. Accordingly, the conventional asynchronous transfer mode system is not effectively operable in the broadcast mode.